A rotary member such as a gear, a driveshaft etc. for transmitting torque of a prime mover to a predetermined portion or member is vibrated inevitably by a torque pulse, a change in a load, and friction and so on, and frequency of vibrations is changed depending on a rotational speed. In this situation, higher vibrations such as secondary vibrations are also generated. Amplitude of vibrations of the rotary member thus generated may be increased by resonance, and if amplitude of the vibrations of the rotary member is increased, the rotary member may be damaged and noise may be increased. In order to avoid such disadvantages, a vibration damper device or mechanism is widely used in various kinds of rotary power transmission devices.
For example, a dynamic damper is known as a device for damping torsional vibrations of the rotary member. In the dynamic damper, a rolling mass is oscillated by torque pulses of a rotary shaft, and the vibrations of the rotary shaft are suppressed by an oscillating motion of the rolling mass. If such oscillation of the rolling mass is restricted by an increase in viscosity of oil or the like, vibration damping performance of the dynamic damper may be restricted. Likewise, if contaminants are interposed between the rotary member and the rolling mass, the vibration damping performance of the dynamic damper may also be restricted.
One example of the dynamic damper adapted to prevent hindrance of oscillation of the rolling mass is described in Japanese Patent Laid-Open No. 2012-197886. According to the teachings of Japanese Patent Laid-Open No. 2012-197886, the dynamic damper is held in a torque converter connected to an output shaft of an engine. The torque converter is provided with a lockup clutch, and an output torque of the engine is delivered to an input shaft of a transmission through the oil and the lockup clutch. Specifically, the dynamic damper is disposed on the input shaft of the transmission inserted into the torque converter. In order not to hinder the oscillation of the rolling mass by the oil in the torque converter, an oscillation range of the rolling mass is covered liquid-tightly by a cover member. The cover member is comprised of an annular first cover member opening toward the engine in an axial direction that is rotated together with a rotary shaft, and a second cover member that is fitted into the opening of the first cover member through a sealing member while being allowed to move in the axial direction. The rolling mass is enclosed by the first cover member and the second cover member while being allowed to oscillate therein. That is, a holding chamber is formed by the first cover member and the second cover, and the holding chamber is sealed liquid-tightly by the sealing member.
Japanese Patent Laid-Open No. 2011-504987 also describes a dynamic damper in which a rolling mass is held oscillatably by a plate member rotated together with a turbine runner of a torque converter. Japanese Patent Laid-Open No. 11-311309 also describes a dynamic damper in which a rolling mass is held in a chamber formed in the torque converter close to an engine. In the chamber, a through hole is formed on a wall of the chamber to provide a connection between an inner space of the chamber and an inner space of the torque converter.
In the dynamic damper taught by Japanese Patent Laid-Open No. 2012-197886 in which the second cover member is fitted into the opening of the first cover member in a movable manner, a pushing force for pushing the sealing member interposed between the first cover member and the second cover member may not be ensured sufficiently. For this reason, a clearance between the first cover member and the second cover member may not be sealed sufficiently liquid-tightly, and hence the oil may intrude into the chamber.
In the dynamic damper taught by Japanese Patent Laid-Open No. 2011-504987 in which the member is held by the plate member, the plate member is basically made of material having relatively high strength. If the chamber is formed by combining a cover member with the plate member made of high strength material, the cover member is not required to have especially high strength and hence the cover member may be made of different metal material. In this case, it would be difficult to connect the cover member to the plate member by a welding method. In addition, if the chamber is formed by attaching the cover members on both sides of the plate member through the sealing member, more bolts are required to compress the sealing member sufficiently. Further, in the chamber in which the sealing member interposed between the cover member and the plate member is pushed from both sides of the plate member, if the plate member or the cover member is inclined for any reason, the cover member may be subjected to a pulling force to be isolated away from the plate member and hence a sealing tightness may not be ensured.